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Could someone please help me identify a burned-up resistor

  1. May 22, 2017 #1
    hi,
    im am hoping someone maybe able to help me identify a resistor the middle is slighty ( fell off) from heat i suspect i will add photos the only coulors left are very end cream then a gold band then cream then middle no there any more then we have a dark brown band then light brown hope that sounds right ?
    one end of the resistor was connected to a diode the diode is a 1n4001 which reads uf=671mv c=11pf

    20170522_121342.jpg 20170522_121426.jpg 20170522_121451.jpg 20170522_121519.jpg
    this came frome a mainboard in a origami stroller i cannot seem to find anything to do with service or schematics
    thankyou for any help
     
  2. jcsd
  3. May 22, 2017 #2

    dlgoff

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    You measured 12.68 KΩ and since heat general will cause a resistor's value to increase, my guess is, it was originally a 10 KΩ resistor.
    But it really depends on how many bands there were originally.
    Color-Coding-Table.jpg
     
  4. May 22, 2017 #3

    davenn

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    tho 12.68 k would still be well within the tolerance range of a 12k resistor :smile:
    and it's either a 1/2W or 1 W rating ... most likely 1/2 watt
     
  5. May 23, 2017 #4

    dlgoff

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    I've never seen a resistor looking like this one staying in specs. Just sayin'
     
  6. May 23, 2017 #5

    davenn

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    you may be right, but I wouldn't discount the possibility :)
    specially since it is a higher wattage one ... if it was only a 1/4 or 1/8 watt, I would 100% agree


    of course a schematic for the unit the thing came out of would help


    soooooo, Carlos ... have you got or searched for a schematic for your device ? .... what is the device, make and model ??


    Dave
     
  7. May 23, 2017 #6

    jim hardy

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    Can you post a picture of what it was removed from?
    4001 is a general purpose power rectifier. Maybe we can guess by tracing out the circuit.

    gold is likely tolerance, 5% per dlgoff's table
    here are standard 5% values per https://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf
    upload_2017-5-23_0-35-17.png

    You'd read bands right to left because tolerance is always last (unless there's a reliability band )
    if that dark brown band was truly brown before overheating
    the only standard values ending in "one" start with a "five" or "nine",
    and first band doesn't appear to be green but maybe was white before cooking....

    so what other possibilities are there ?

    To make a whole Watt across 12k ohms would require about 109 volts.
    Is the circuit capable of that?
    If not, your resistor was considerably lower ohms before the smoke got out of it.

    Those are some thought steps toward figuring out your puzzle.
     
  8. May 23, 2017 #7

    dlgoff

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    Check out the pictured socked he used. I believe it's this one (from https://www.digikey.com/catalog/en/partgroup/textool-series/7883 ). Note the hold spacing, which to me, says it's not a physically big resistor.


    214-3339-00-0602J.jpg
     
  9. May 23, 2017 #8

    davenn

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    I seriously doubt that that is the device the resistor came from ... hence why I asked for the device make and model
    it's a tester that is giving a test value

    and the size of the resistor is better gauged by its appearance with the diode, a standard 1N4xxx and it's much bigger than the diode
    I still go with the at least 1/2 watt rating
     
  10. May 23, 2017 #9

    dlgoff

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    Good point.
     
  11. May 23, 2017 #10

    dlgoff

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    I was just speaking of his tester device that I pictured. But you may be right about it being a 1/2 watt.
     
  12. May 23, 2017 #11
    thankyou for all the replys it is appreciated this came out of an origami stroller (its a pram that folds its self up and down) i can not find any schematics it runs on a 11.1v lithium battery at 1A
    this is the board circled in red is where the diode and resistor was pulled from.....
    Capture.png
    and this is what it came from
    About the product
    • Opens and closes itself at the touch of a button
    • Self-charging via generators in the rear wheels
    • Daytime running lights. Automatic pathway lights
    • LCD dashboard including thermometer, speedometer, trip and lifetime odometers
    814BY%2BCgzqL._SX522_.jpg
    looking at the board the resistor was the only thing that looked wrong there was power to the board but nothing was working so im just going though the process of elimination The chap i bought it from said there was no charger so thinking he just tryed one and that is what fryed the resistor when testing the battary it was charged to 11.5v but then this buggy charges its self when being pushed

    again thans for all your help.
     
  13. May 23, 2017 #12
    Interesting puzzle. So far the most useful guesses to me are those made by @dlgoff in comment #2 and @jim hardy in #6. Clearly this is a smallish power resistor compared to all those SMC's on the board. I too searched for a schematic and/or service manual (yes, I have a lot of time on my hands some mornings) and like the OP I came up empty.

    As Jim points out, that sort of diode is often associated with a power supply. A DC battery wouldn't require rectification, but what about a generator working off the wheels (wild guess)? If the OP (@carlos468) were extremely obsessive-compulsive and had no other real-world responsibilities to attend to (e.g. no job, wife, or child), he could sketch a partial layout (and from that a schematic) for that part of the board, getting values for other nearby components by inspecting them; hopefully the board is no more than double-sided, which means you'd still have to look for via's (little holes which connect traces on the opposing sides) and also identify the ground plane. You wouldn't have to do the entire board, just enough that someone could take a good guess at this part of the circuit. I once drew both sides of a PCB for a guitar amplifier, just so I could analyze the layout; so it can be done.

    However - one thing that gives me pause is, the fact that the resistor burned out in the first place - as the OP says, apparently when the previous owner somehow plugged a charger in (no details given by the OP on what this entailed). Sometimes a resistor will literally "take the heat" and protect the rest of a circuit by burning open, almost like a fuse; but often even when that is the design intent, it isn't always enough. Thus the possibility exists that even as the resistor was toasting, more sensitive components such as ICs and transistors were getting killed; typically this happens without leaving visible evidence. Possible support for this theory is that if the resistor still measures as having resistance, rather than being open-circuit, that means it didn't get sufficiently fried to stop conducting or even to alter its value as hugely as it might have; which in turn may mean that it's not be to blame for the circuit not working. I am guessing there are at least transistors on that board, as I see a lot of three-legged creatures in the photo that seem to have "Q" associated with their part label; but that's just a guess as my solid-state knowledge is pretty limited.

    At any rate I would be wary of committing a huge amount of time to worrying about exactly what resistor it was, without a better sense of what the previous owner did as well as a plan for identifying and checking the status of the semiconductors on the board. Without a schematic and some experience at checking voltages for transistors & ICs and so forth it would be very difficult to tell. You could just get yourself a half-watt 10K resistor and a new diode and solder them in place & see what happens. If no joy, then the most efficient option might be to find a service shop that could at least take a quick look (good service shops will do that). Some product companies will supply replacement boards to repair shops; others won't. But this little board looks simple enough that potentially a capable repair shop could replace bad parts and get it running again.
     
    Last edited: May 23, 2017
  14. May 23, 2017 #13
    thankyou for the reply UsableThought i may have to sketch a partial layout but i may go for the bung a 10k resistor on the board and see what happens :) this board has a clear film (glue) over it i would say it was for water proofing so putting a solding iron to it is not very nice i think if that does not work ie putting a 10k resistor on it imay then go for the capacitors they dont look bad but im thinking for what there is on the board it wouldnt be a hard ship to swap the whole lot for new i was just a bit stuck on the resistor
    but open to ideas and help thankyou all again :)

    more photos
    1.jpg
    2.jpg
    3.jpg
    4.jpg 5.jpg
     
  15. May 23, 2017 #14
    Do you mean the SMC caps, or the big electrolytics?

    When big electrolytics get subjected to reverse polarity, typically you will see damage - the ends bulge or leak goo; or even explode. If subjected to excess voltage that is high enough, my guess is you'd also see damage. If you don't see this sort of thing those caps are probably fine.

    My own opinion is that caps are the least likely component to be your problem. I speak from limited but relevant experience: aside from troubleshooting various cap/resistor issues in a guitar amplifier built mostly on a PCB, I once subjected a small battery-powered audio amplifier to an over-voltage input & had to troubleshoot that as well. I was lucky enough to locate a schematic; plus I had an excellent DIY book on how to repair solid state consumer electronics. I then checked the circuit's single transistor and single IC to see if they registered expected voltages; they did not, so I replaced them & the amp worked again. It's key to know what voltages you should be getting when you check particular nodes against ground w/ a voltmeter.

    Again, if replacing the resistor doesn't help and you don't have a methodical plan of repair based on at least a basic understanding of consumer solid state circuits, you are likely to be wasting your time. Of course it's your time to do with what you wish; but I would suggest doing what you can to make it a learning experience rather than just a frustrating experience. E.g. if this sort of thing is new to you, maybe get a book of the sort I linked to above & start reading. Forums can't teach you everything.

    P.S. As for the waterproof coating, just chip or scrape it off the areas you want to work on, being careful not to damage traces. Shouldn't be a problem if you work carefully.
     
    Last edited: May 23, 2017
  16. May 23, 2017 #15

    davenn

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    that's what I said !!

    yes so ?

    probably, very wild .... diodes are used for lots of other purposes other than just rectification
    it could just as easily be used for polarity reversal protection



    it definitely wouldn't hurt and it would be interesting to see what happens, just be ready to pull the power connection quickly

    yeah, some of those conformal coatings can be yucky

    can you please take 2 more pic's of the board, closer up ... take care with the focus, well lit. If the pic doesn't look clear to you once taken
    try doing another pic till it loos good before uploading :smile:
    and just the left hand side of the board from the edge and up to those 2 higher power resistors. Both sides of the board in that area


    Dave
     
  17. May 23, 2017 #16
    No slight intended; I liked the comments I mentioned for their overall perspective. And certainly the diode could be for another purpose; it's just that I am tickled by the thought that this stroller charges itself by being pushed.

    Also, for the benefit of @carlos468 - I assume that when you advise being "ready to pull the power connection," you mean to turn the scooter off (and remove the battery) if either (a) he smells smoke, or (b) the stroller's electronic functions don't immediately come back to life? Smoke seems unlikely with just the lithium battery, but I agree, if no signs of life kill power on general principles.
     
    Last edited: May 23, 2017
  18. May 23, 2017 #17
    thanks again for taking the time to reply
    Dave i have taken the photos you asked for hope they are ok
    1a.jpg 1b.jpg 2a.jpg 2b.jpg 3a.jpg 3b.jpg
     
  19. May 23, 2017 #18
    Take a closer look at the "LEG2" connector with the black and white wires - it appears to be a bit smashed up. There are two "LEG" connectors, and I'm guessing they go to DC generators built into the rear wheels.

    One trick when powering up dead, "black box" boards (ones that you don't have schematics for) is to carefully mark and record how all wiring is connected, disconnect everything except for the power supply, then flip the switch. If nothing blows up, the board itself probably doesn't have short-circuited components. Individually reconnect each wire connector, re-test, and repeat until all wiring has been reconnected. If things go awry after the nth cable has been reconnected, that's a good place to focus on.
     
  20. May 23, 2017 #19
    yes i tested that for continuity as the leds for that just go to a little jack plug (i agree the board and plugs And soldering look abit naff for an $800 buggy) anyway i think that one is for little leds at the front, thing with unpluging and trying one at a time is the lcd near the handlebars should come on as soon as you move the stroller or as soon as you twist a knob on the handlebars there is a button in the middle of that knob that makes the stroller go up and down but nothing works at all
    here are a couple of photos of it still in the buggy
    32.jpg 33.jpg

    im going to try and do a photo of the board listing where all the wires feed too thanks to all for the help and advice
    as you all seem really helpful i would also like to write what i have done and going to do and fingers crossed i can get this little thing working as is should :)
     
  21. May 23, 2017 #20

    jim hardy

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    Did i see the resistor and rectifier joined up in the air, above the board ? As in parts added after the board was built ? Which means they're a fix for some "Design Oops" ?

    That sounds like either:
    a 'flywheel' diode for an inductor such as a motor.
    or
    reverse polarity protection across a voltage regulator IC, to keep a downstream filter capacitor .from discharging backward into the regulator's output terminal on power down, which could become forward biased should he attempt to charge with a wrong polarity charger..... That'd wreck the voltage regulator and if he's real lucky nothing else.


    Another observation Carlos can make:
    Look at those capacitors on the board, the round cans wrapped in plastic. What voltage is printed on them ?
    If none are marked 100 volts or more, then i don't think there's enough voltage on this board to possibly hurt a 10K resistor and I'd suspect it was closer to 10 or 100 ohms before cooking.

    What do you guys think about replacing the resistor with a 1/10 amp 12 volt lamp ? With a millivoltmeter he could see what traces are carrying high current.

    For just measuring, I use a straight pin from Fair Anne's sewing basket as a meter probe to push through that varnish-ey stuff.
     
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